ETH_Informatik/Informatik_I/Exercise_1/Task_1

Task 1: Expressions

• Task
• Solution

Task

Let a, b, c, and d be variables of type int.

• Which of the following character sequences are valid expressions in the sense that they are accepted by a C++ Compiler? Explain your answer.

1. a = b = 5
2. 1 = a
3. a + b
4. a + b = c + d
5. a = 2 b

Assume that all the variables have been defined and correctly initialized and that all expressions are completely independent from each other.

• For each of the expressions that you have identified as valid, decide whether the entire expression is an lvalue or an rvalue, and explain your decision.
• Determine the values of the expressions that you have identified as valid and explain how these values are obtained.

Solution

# Task 1

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### Expression 1: `a = b = 5`

The expression is valid and will be accepted by the CPP compiler. It will result with the l-values `a = 5` and `b = 5`. This is due to the fact the the `=` opperation is read from right to left so `b = 5` will run first and `a = b` afterwards.

### Expression 2: `1 = a`

The expression is invalid.

### Expression 3: `++a + b++`

The expression is valid and will be accepted by the CPP compiler. It will result in a r-value since the result is not assigned to a variable.

### Expression 4: `a + b = c + d`

The expression is invalid.

### Expression 5: `a = 2 b`

The expression is valid and will be accepted by the CPP compiler. It will result with the l-value `a = 2 b`. This is valid since a l-value can be a r-value.

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Made by JirR02 in Switzerland 🇨🇭